This proposal requests support for a shared quadrupole gas chromatograph mass spectrometer instrument to permit the measurement of stable isotopes in biological materials. Institutional financial, space, and technical support have been committed for this project and have already made possible the purchase of an isotope ratio mass spectrometer. The proposals of 6 PHS-funded investigators who will use the facility are submitted; 4 are currently doing PHS-funded stable isotope work. Included are: (1) Griggs (Principle Investigator) whose work involves the measurement of whole body leucine kinetics and the incorporation of 13C leucine into skeletal muscle protein in patients with neuromuscular disease and in normals. (2) Nair (Laboratory Director) whose preliminary data in type I diabetic patients and normal control subjects suggest that insulin's main action on protein metabolism is to decrease proteolysis, and glucagon's to increase leucine oxidation. His work will also examine the relationship between indirectly calculated whole body protein synthesis and the incorporation of L-(1-13C) leucine into skeletal muscle protein and into plasma protein. (3) Welle will study the effect of the changes in energy balance on protein metabolism using L-(1-13C) leucine as a tracer and on glucose metabolism using 6,6 2H2 glucose. (4) Moxley will study the effect of insulin on skeletal muscle amino acid metabolism by using L-(1-13C) leucine as a tracer for forearm studies conducted during graded euglycemic insulin infusions. (5) Amatruda and Sparks will use stable isotopes in animal studies to directly measure apolipoprotein synthesis and will explore their use for studies of apolipoproteins in normal man and in disease states. We have investigators with expertise in measuring isotopic abundance in plasma, expired air, and tissue samples. The isotope ratio mass spectrometer which we are obtaining will permit us to measure the isotopic abundance (13C/12C) of 13C02 in expired air and the ninhydrin-liberated 13CO2/12C02 ratio of amino acids in tissue protein. In order to pursue studies of plasma isotopic abundance we must have a gas chromatograph mass spectrometer with chemical ionization and electron impact ionization modes, which can determine negative ions, and handle both packed and capillary columns. The laboratories of Halliday and of Matthews have made possible our current studies using stable isotopes but cannot handle the expanded number of samples form our investigations.